The present invention relates to low observable materials, and more particularly relates to electromagnetic wave absorbing materials comprising magnetic alloy particles and an insulating matrix. The materials may be used in the form of coatings for applications such as hot engine exhaust areas of aircraft.
Radar absorbing materials have been developed for various applications, such as for use in hot engine exhaust areas of aircraft. Iron powder has been proposed for radar absorbing coatings. However, iron is susceptible to oxidation at elevated temperatures, e.g., 1,100xc2x0 F. and higher.
U.S. Pat. No. 5,574,961 to Edelstein et al. discloses a radar absorbing material comprising Fe and/or Co in combination with boron nitride.
Several methods of preparing and applying microwave absorbing materials currently exist. However, conventional materials require specialized equipment or procedures, and are not easily repairable in the field. Aircraft are often assigned to remote areas and require routine maintenance. Present methods require special equipment, facilities and trained personnel to apply materials.
An electromagnetic wave absorbing material that is capable of functioning at high temperatures would be desirable. Furthermore, an electromagnetic wave absorbing material that is relatively easy to apply to components would facilitate its use in controlled or remote locations.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
The present invention provides an electromagnetic wave absorbing material comprising magnetic alloy particles and an insulating matrix. The magnetic alloy particles comprise a transition metal such as Fe and/or Co, and further comprise at least one refractory metal such as Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W. The magnetic alloy particles may further include Ni and/or Al, or any other alloying additions which provide the desired absorption characteristics. In a preferred embodiment, the magnetic alloy particles comprise an Fexe2x80x94Crxe2x80x94Nixe2x80x94Al alloy. The insulating matrix of the electromagnetic wave absorbing material may comprise a refractory cement. The material may be provided in the form of a coating which may be applied to a substrate, such as a hot engine exhaust area of an aircraft. The electromagnetic wave absorbing materials of the present invention are capable of functioning at very high temperatures for extended periods of time while retaining satisfactory electromagnetic wave absorbing properties.
Another embodiment of the present invention provides a method of making an electromagnetic wave absorbing material coating. The method includes the steps of mixing magnetic alloy particles and insulating matrix precursor particles, combining the mixture with a liquid such as water to form a slurry, and applying the slurry on a substrate. The slurry may be applied by spraying or the like.
An aspect of the present invention is to provide an electromagnetic wave absorbing structure comprising a substrate and an outer layer of electromagnetic wave absorbing material over at least a portion of the substrate. The electromagnetic wave absorbing material comprises an insulating matrix and magnetic alloy particles in the insulating matrix, the magnetic alloy particles comprising at least one transition metal selected from Fe and Co, and at least one refractory metal selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W.
Another aspect of the present invention is to provide an electromagnetic wave absorber that is capable of performing electrically and structurally in an engine exhaust environment or the like.
A further aspect of the present invention is to provide small particle alloy powder that is substantially spherical, multi-grained and has desirable magnetic properties.
Another aspect of the present invention is to provide an electromagnetic wave absorbing material that is capable of operating in a broadband frequency range.
Another aspect of the present invention is to provide a radar absorbing material that will adhere structurally to typical aircraft engine components and the like.
A further aspect of the present invention is to provide a radar absorbing material that can function at high temperatures.
Another aspect of the present invention is to provide a radar absorbing coating that is capable of absorbing microwave energy at certain frequencies by controlling the proportion of magnetic alloy particles used in the coating and by controlling the final thickness of the coating.
A further aspect of the present invention is to provide a method of making an electromagnetic wave absorbing material coating. The method comprises mixing magnetic alloy particles and insulating matrix precursor particles, combining the mixture with a liquid to form a slurry, and applying the slurry on a substrate to form an exposed coating of electromagnetic wave absorbing material comprising the magnetic alloy particles in the insulating matrix.
These and other aspects of the present invention will be more apparent from the following description.